fixed compile error complaining about literal "null"
fixed compile error complaining about literal "null"

neobrain/aeson,jkarni/aeson,roelvandijk/aeson,sol/aeson,abbradar/aeson,sol/aeson,bwo/aeson,plaprade/aeson,SeanRBurton/aeson,timmytofu/aeson,roelvandijk/aeson,lykahb/aeson,23Skidoo/aeson,aelve/json-x,JPMoresmau/aeson,beni55/aeson,sol/aeson,dmjio/aeson,nurpax/aeson,neobrain/aeson